Summary translation

Since heterogeneous soil conditions are present almost everywhere, the correct choice of experimental site affects the conduct of field trials and the interpretation of the results. The soil of the Experi¬mental Farm for Organic Agriculture "Wiesengut" located at Hennef near Köln-Bonn (classification: Fluvisol - FAO; Udifluvent - USDA) is characterized by a pattern of soil variability which can vary even within several metres. Therefore the area of farmland which can be used for factorial field trials is restricted. In order to select the most suitable experimental area, a database has been worked out composed of data sets related to: Surveying - Mapping: Differences in crop development caused by hetero¬geneous soil conditions had been marked in the field during regular crop moni¬toring sessions. Maps of different scale and content were drawn up, based on electronic distance and angle measurements to provide the correct spatial relation of soil variability. Aerial photography: Multitemporal and multispectral aerial photography at low altitude provided an essential basis for characterizing soil-affected crop growth and development. Uniformity trials: Areas that seemed visually suitable for field trials were harvested in small units by hand and combine harvester to quantify the soil heterogeneity by plant yield parameters. The recor¬ded data create a valuable resource, enabling increased precision to be achieved by selecting the most efficient field plot design. Coefficient of variation (cv %) for kernel and total yield of cereal were between cv = 10 - 25 and could be reduced to cv = 3 - 10 by selecting visually homogeneous areas. Interannual coefficients of correlation for yield parameters of heterogenous areas were placed bet¬ween r = 0,2 - 0,8 to r = 0 - 0,5 for visually homogeneous sites. Low yielding areas and winter cereals showed higher coefficients of variation and higher interannual coefficients of correlation. The general suitability of the methods and techniques used for characterizing heterogeneous soil condition are discussed. Currently used plot designs and methods of statistical analysis are not very efficient in compensating for soil variability. Further improvement is urgently required. The next step in optimizing field plot research on the Experimental Farm Wiesengut will be the definition of fixed field plot patterns in areas having low soil variability in order to select the most suitable areas and best adapted experimental designs.